import to Catalog forces auto sync to file - why?

[BrianS]

I have just discovered that if I use Import To Catalog the file is automatically being synced being written to (I noticed the file mod date and 'Software' exif data had been changed to "Photo Supreme Ver 6.0.4.###"

In the my current bunch of imports I am only adding one or two Labels on each import, (I am doing a backlog of a few years of images on the PC).
in Preferences "Automatically write out Catalog changes to the image file" is not ticked. So why does PSU do this (auto sync) on an Import?
I tested doing an Import that does not apply a label or anything else - bingo PSU didn't auto sync.

My problem is that I should be able to choose when I sync my files including after Import. BTW drag and drop does not do this, but of course I can't apply labels etc automatically that way.

I guess I could turn on "only write metadata to Catalog" but I don't know what will happen if I turn this back on. I will eventually want to sync to the files, I just don't want PSU to do it without my permission.